1. Field of the Invention
This invention relates to a control system for a photographic apparatus and more particularly to a control system for photographic apparatus wherein the control system embodies galvano-magnetic effect switching devices.
2. Description of the Prior Art
Thin and compact photographic cameras of the reflex type have been developed wherein the exposure of the film unit is electronically controlled and the film unit may be rapidly processed at a processing station within the photographic camera. A version of such a camera having a compactness and thinness suited to permit convenient carrying in the pocket of a garment is described in a U.S. Pat. entitled "Reflex Camera" by E. H. Land, No. 3,672,281. Such cameras are of the single lens reflex variety and require a complex exposure control system in order to accommodate a requisite viewing and focusing mode during which time the single lens reflex camera is in a normally open status to unblock the passage of light through the exposure opening to a viewfinder. At the commencement of an exposure cycle, the shutter mechanism of the camera exposure control system is driven into a closed or light blocking orientation by a tractive electromagnetic device whereupon the photographic camera is automatically operated to change from the viewing and focusing mode to an exposure mode in which photosensitive film is made accessible to the optical path of the taking lens of the camera. When the camera has assumed the exposure mode of operation, the exposure control system operates to release a shutter mechanism from its light blocking orientation wherein such exposure control parameters as exposure interval and aperture size are controlled as a function of scene brightness as evaluated with respect to the sensitometric characteristics of the film being exposed. At the termination of the electronically determined exposure interval, the shutter is again driven to a fully closed or light blocking position to terminate exposure until such time as a camera reassumes the viewing or focusing mode.
Single reflex photographic cameras embodying the above-described exposure control system are suitable for use with film units described in detail in U.S. Pat. to E. H. Land, No. 3,415,644 entitled "Novel Photographic Products and Processes". Such film units include all the materials necessary to produce a positive photographic print by an image-forming process which is now well known in the art and involves the formation of transverse image-forming substances in an exposed photosensitive element by their diffusion in a manner forming a visual positive image.
Exposure mechanisms of such photographic cameras generally include at least two cooperatively moving shutter blades which ride transversely within supporting tracks. The blades are formed with selectively shaped aperture openings which, depending upon the position of the blades, symmetrically overlap over a light entering exposure opening within the camera housing. Such blades may be connected to define a progression of apertures over the light entering opening in the camera as a result of their connection with a so-called "walking beam" which is rotatably mounted with respect to the camera housing. The "walking beam" is selectively rotated through a tractive electro-magnetic device such as a solenoid, the plunger of which is arranged to actuate a mechanical switch upon full retraction thereof. The mechanical switch in return provides a signal to the exposure control system indicative of when the shutter blades have been moved into a closed terminal position. The use of a mechanical switch in the above-described manner, although entirely satisfactory for its intended purpose, incurs one drawback due to the production of bounce when the contact is closed. Such bounce is, of course, undesirable and would preferably be eliminated. A second problem that exists is a tendency for a mechanical switch to have a relatively limited life when compared to the invention of the present application.
Therefore, it is a primary object of this invention to provide a reliable exposure control system for a photographic apparatus where at least one mechanical switching device in the exposure control system can be eliminated.
It is also an object of this invention to provide a reliable exposure control system for a photographic camera apparatus wherein a galvano-magnetic effect switching means may be used in place of a mechanical switch.
It is a further object of this invention to provide a reliable exposure control system for a photographic camera apparatus wherein the adverse effects generally associated with the bounce of a mechanical switch as hereinbefore utilized may be eliminated by a galvano-magnetic effect switching circuit embodying a Hall effect switching device.
It is an even further object of this invention to provide a reliable exposure control system for a photographic camera apparatus wherein the useful life of the control system may be increased by substituting a galvano-magnetic effect switching circuit embodying a Hall effect device in place of a mechanical switch as heretofore used.